Update docs.yml

Author: ViralBShah

.github/workflows/docs.yml

@@ -18,7 +18,7 @@ jobs:
         julia-version: [1]
         os: [ubuntu-latest]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@latest
         with:
           version: ${{ matrix.julia-version }}